Details are given of an inexpensive force plate designed to measure ground reaction forces involved in human movement. Such measurements provide interesting demonstrations of relations between displacement, velocity, and acceleration, and illustrate aspects of mechanics that are not normally encountered in a conventional mechanics course, or that are more commonly associated with inanimate objects. When walking, the center of mass follows a curved path. The centripetal force is easily measured and it provides an upper limit to the speed at which a person can walk. When running, the legs behave like simple springs and the center of mass follows a path that is the same as that of a perfectly elastic bouncing ball.
REFERENCES
1.
M. J. Adrian and J. M. Cooper, Biomechanics of Human Movement, 2nd ed. (Brown and Benchmark, Madison, Wisconsin, 1995).
2.
R. M. Alexander, The Human Machine (Natural History Museum Publications, London, 1992), pp. 59–87.
3.
R. M. Alexander, Exploring Biomechanics: Animals in Motion (Scientific American Library, distributed by W. H. Freeman, New York, 1992), pp. 17–55.
4.
J. Rose and J. G. Gamble, Human Walking, 2nd ed. (Williams and Wilkins, Baltimore, 1996), pp. 1–99.
5.
Available from Thomson Marconi Sonar P/L, 274 Victoria Rd., Rydalmere NSW 2116 Australia; electronic mail: [email protected].
6.
It is a common observation, when someone slips on a banana skin, that the front foot slips forward.
7.
A.
Crowe
, P.
Schiereck
, R. W.
de Boer
, and W.
Keeson
, “Characterization of human gait by means of body center of mass oscillations derived from ground reaction forces
,” IEEE Trans. Biomed. Eng.
42
, 293
–303
(1995
).8.
J.
Nilsson
and A.
Thorstensson
, “Ground reaction forces at different speeds of human walking and running
,” Acta Physiol. Scand.
136
, 217
–227
(1989
).9.
A.
Crowe
, M. M.
Samson
, M. J.
Hoitsma
, and A. A.
van Ginkel
, “The influence of walking speed on parameters of gait symmetry determined from ground reaction forces
,” Human Movement Sci.
15
, 347
–367
(1996
).10.
For the same reason, the time average weight of a 70 kg person juggling three 1 kg balls in the air is 73 kg weight.
11.
T. A.
McMahon
, G.
Valiant
, and E. C.
Frederick
, “Groucho running
,” J. Appl. Physiol.
62
, 2326
–2337
(1987
).12.
G. A.
Brett
and R. T.
Whalen
, “Prediction of human gait parameters from temporal measures of foot-ground contact
,” Med. Sci. Sports Exercise
29
, 540
–547
(1997
).13.
J. G. Hay, The Biomechanics of Sports Techniques, 3rd ed. (Prentice–Hall, Englewood Cliffs, 1985), pp. 395–414.
14.
R. Cross, “The bounce of a ball,” Am. J. Phys. (accepted for publication).
This content is only available via PDF.
© 1999 American Association of Physics Teachers.
1999
American Association of Physics Teachers
AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.
